The strength of a rectangular beam varies jointly as its width and the square of its depth. If the strength of a beam 4 inches wide by 12 inches deep is 1800 pounds per square inch, what is the strength of a beam 5 inches wide and 12 inches deep?

Answer 1

using the first letter for each variable ...
S = k (w*d^2)
plug in the 3 given values to find k, rewrite the equation, replacing k
then find the missing variable for the second set of data .